I got my hands on a littleBits starter kit! I wrote about littleBits previously and posted their intro video. The finished pieces work well and are a fun way to explore electronics.
My friends' third grader came over and we explored the littleBits pieces.
Because the parts are magnetized it is impossible to put them together "incorrectly." His first attempt, above, did not produce the results he was looking for, and he was able to rapidly modify the design of his circuit and make the buzzer buzz.
I love how he immediately thought of how he could integrate littleBits into his LEGO creations.